Group training system for electronic musical instruments

ABSTRACT

A group training system for electronic musical instruments including a teacher station and a plurality of student keyboard instrument stations wherein the teacher station has a plurality of tone generators corresponding to one octave of musical notes. Each tone generator is connected to a first divider chain including a plurality of cascade connected frequency dividers. The outputs of the tone generator and the frequency dividers are selectively supplied through a multithrow switch operable by the teacher to a second divider chain similarly including a plurality of cascade connected frequency dividers. The signals successively frequency-divided by the dividers of the second chain, as well as the input signal thereto, are all fed to each student station to provide a certain range of musical notes. Where the teacher operates the multithrow switch, the frequency of the input signal impressed on the second divider chain varies, resulting in a change in the performance compass of the student stations. The input signals impressed on the second divider chain may be varied for groups of the student stations to enable ensemble performance.

United States Patent 1191 Okamoto Feb.5,1i974 [75] Inventor: EisakuOkamoto, Hamakita, Japan [73] Assignee: Nippon Gakki Seizo KabushikiKaisha, Shizuoka-ken, Japan 22 Filed: Aug. 8, 1972 [21 App]. No.:278,823

[30] Foreign Application Priority Data Primary Examiner-Lawrence R.Franklin Attorney, Agent, or Firm -Kemon, Palmer & Estabrook [57 IABSTRACT A group training system for electronic musical instru mentsincluding a teacher station and a plurality 01' student keyboardinstrument stations wherein the teacher station has a plurality of tonegenerators corresponding to one octave of musical notes. Each tonegenerator is connectedto a first divider chain includ ing a plurality ofcascade connected frequency dividers. The outputs of the tone generatorand the frequency dividers are selectively supplied through a multithrowswitch operable by the teacher to'a second divider chain similarlyincluding a plurality of cascade connected frequency dividers. Thesignals successively frequency-divided by the dividers of the secondchain, as well as the input signal thereto, are all fed to each studentstation to provide a certain range of musical notes. Where the teacheroperates the multithrow switch, the frequency of the input signalimpressed on the second divider chain varies, resulting in a change inthe performance compass of the student stations. The input signalsimpressed on the second divider chain may be varied for groups of thestudent stations to enable ensemble performance.

11 Claims, 7 Drawing Figures Aug. 9, 1971 Japan 46/70440 Mar. 21, 1972Japan 47/3230] Mar. 21, 1972 Japan 47/32302 [52] US. Cl. 84/470 [51]Int. Cl. G09b 15/00 [58] Field of Search 84/445, 454, 470, 477-482 [5 6]References Cited UNITED STATES PATENTS 3,470,785 10/1969 Shallenbergeret a]. 84/470 2,924,776 2/1960 Peterson 84/454 X 3,482,480 12/1969Decker 84/478 3,501,850 3/1970 Oachterlony 84/478 3,584,530 6/1971Andersen 84/470 3,674,907 7/1972 Derry 84/445 X FREQUENCY 12 DlVJlgERTEACHER STATION 1 TO OTHER STUDENT STATION g PATENTEUFEB 51974 3.789.723

SHEEI 1 0f 4 TONE GENERATORS H c cg FREQUENCY DIVIDER HIGH TEAcHER MIDDSTATION I TO OTHER STUDENT STATION KEY SWITCH STUDENT STATION 2 TONEGEN.

C? F I G. 2

I2 HIGH I4-/ .9 MI' DI \f I [LOVE +2 +2 +2 D TO FIRST GROUP 13-/Z2 A EOF STUDENT STATIONS I c TO SECOND GROUP B A f 20 3 +2 +2 +2 D I g TOTHIRD GROUP I4-n I -2 -2 -2 TO n- Th GROUP PATENIEDFEB 5 m4 SHEET 3 0F 4IFIG.4

DIVIDER CHAIN DIVIDER CHAIN DIVIDER CHAIN ?ATENTEBFB sum SHEET l BF 4FIG.5

CABLES STUDENT STATION TEACHER STATION 2. i

FIG.6

IFIG.7

CABLES STUDENT STATION 2 N w T A T S E H C A E T TO OTHER STUDENTSTATIONS GROUP TRAINING SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTSBACKGROUND OF THE INVENTION ,a group training system for keyboardmusical instruments, particularly electonic organs. This system includesas many as 20 to 30 student stations formed of musical instruments asagainst a single teacher station. The students practice performance ontheir musical instruments under the teachersinstructions. Though studentstations may consist of a type .having'tone generators of its own, thereoccur considerable difficulties in attaining agreement among the pitchesof the same categories of tones obtained from the electronic musicalinstruments of the teacher and students.

In the group training system for muscial instruments, therefore, tonegenerators are all provided in the teacher station alone, and tonesignals from the tone generators are distributed to the studentstations. The

tone signals supplied to the student stations are conducted upon keydepression by the students through key switches to the electroniccircuits, for example, tone coloring filters and amplifiers of thestudent stations finally to operate the loudspeakers or headphones.Installation of tone generators only in the teacher station attainscomplete accord among the pitches of the same categories of tonesproduced-by all the musical instruments installed in the class room, andmoreover prominently simplifies the musical instruments played by thestudents.

However, more transmission of tone signals from the teacher station tothe student stations always gives forth the tones having-the identicalpitch when the identical keys of the studentstations are depressed.Where, therefore, there is to be played an ensemble performance bydividing the student stations into same I groups and causing the groupsto undertake performances of the high, medium and. low pitchesrespectively, then the teacher should inform the students of each groupof that portion of the keyboard which they are requested to operate.

Musical instruments generally used for group training consist of a smalltype bearing, for example 49 keys. Such a small musical instrument has anarrow compass of tones and is undesirable for an ensemble performance,imposing limitations on a group training system for musical instruments.

It is accordingly an object of this invention to provide a grouptraining system or musical instruments which enables the teacher freelyto vary the compass of the student stations and consequently an ensembleperformance to be attained even when the students operate the same partof the keyboards of their musical instruments.

Another object of the invention is to provide a device by whicheach'student is informed of the compass of tones with which he is makinga performance.

SUMMARY OF THE INVENTION A teacher station used in a group trainingsystem for electronic musical instruments according to this invention isprovided, like an-ordinary electronic musical instrument, with tonegenerators corresponding to 12 notes included in the high octave.

Each tone generator is connected to a plurality of frequency dividersarranged, for example, in two-stage cascade formation. Outputs from thetone generators and frequency dividers selectively pass throughmultithrow 'switches to divider chains each consisting of a plurality ofcascade connected frequency dividers. All the above-mentioned frequencydividers divide the frequency of input signals by two. Outputs from thefrequency dividers included in said divider chains are conducted to thestudent stations by cables so as to be used as octavelly related tonesignals for the same note of the student stations. The aforesaidmultithrow switch is changed by the teacher according as he choosesstudent stations to have a high, medium or low compass. Thus, even whenthe students operate the identical part of the keyboards of theirmusical instruments, the resultant tones will have the pitches varied tothe high, medium or low level.

Further, according to this invention, there are provided lamps at suchspots easily observed by the students that are close to the keys of thekeyboards of the student stations corresponding to a referential note,for example, the note C For a 49-key musical instrument, three lampswill fully serve the purpose. Upon operation of the multithrow switch bythe teacher, one of the lamps is turned on. For example, where theteacher chooses the high compass, a lamp on the extreme left, that is,the one positioned at the lower pitch side is operated to inform thestudents that their musical instruments are used for a high compassperformance. Conversely where the teacher desires the students to make alow compass performance, then there is lighted a lamp on the extremeright, that is, the one disposed on the higher pitch side. To this. end,the three, lamps of each student station are connected to a power sourcethrough four lines and a switch provided in the teacher station which isinterlocked with the aforesaid multithrow switch. Or if there is used anelectronic circuit of the present invention, it will be possibleselectively to turn on any one of the three lamps by connecting theteacher station and student stations using a pair of lines.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a grouptraining system for electronic musical instruments according to anembodiment of this invention;

FIG. 2 is a block diagram of the tone generator and frequency dividerarrangement of the teacher station where it is used for an ensembleperformance on the student stations;

FIG. 3 is a block diagram of the tone generator and frequency dividerarrangement of the teacher station attaining a better ensembleperformance than that of FIG. 2;

FIG. 4 is a block diagram of a switching mechanism employed in thesystem of this invention;

FIG.'5 is aschematic plan view of a student station provided with lampsfor indicating the variation of compasses;

3 FIG. 6 represents a connection diagram according to an embodiment ofthis invention for indicating the variation of student station compass;and

FIG. 7 shows a circuit diagram according to another embodiment of thisinvention for indicating the variation of student station compass.

DESCRIPTION OF THE PREFERRRED EMBODIMENTS As illustrated in FIG. 1, ateacher station 1, like an ordinary electronic musical instrument, has12 tone generators corresponding to l2 notes included in the highestoctave, for example, notes C C fi, D7, D E, F7, F 5, G1, CW7, A A and BThe reference numeral 11 denotes one of the tone generators whichproduces tone signals corresponding to note C An output from the tonegenerator 1 1 is supplied to the input side of a first divider chainconsisting of cascade connected frequency dividers 12 and 13. Outputsfrom the tone generator 11, and frequency dividers 12 and 13 areconducted to the three fixed contacts a, b and c respectively of atriple throw switch 14. The frequency dividers 12 and- 13 divide thefrequency of input signals by two. Accordingly, there are obtained tonesignals corresponding to the notes C C and C on the output sides of the'tone generator 11, and frequency dividers 12 and 13.

The movable contact of the triple throw switch 14 is connected to theinput side of a divider chain 20 consisting of three cascade connectedfrequency dividers l5, l6 and 17. From the movable contact of the triplethrow switch 14 as well as from the output sides of the frequencydividers 15, 16 and -17, there are drawn out octavelly related outputsA, B, C and D associated with the note C. These outputs and similar fouroctavelly related outputs associated with the other tone generators aresupplied to the student stations 2 by cable. Tone signals from theteacher station 1 are conducted throughthe corresponding key switches tothe electronic circuits of the student stations 2, for example, tonecoloring filters and amplifiers.

Generation, as shown in FIG. 1, of four octavelly related tone signalsfor each note by the frequency dividarranged as illustrated in FIG. 4.Namely, each switching means connected to the divider chain 20 consistsof two series-connected double throw switches 40A and 40B controlled byrelays 41A and 41B respectively. One fixed contact of the first switch40A is connected to the output terminal of the tone generator 11 and theother fixed contact of the switch 40A is connected to the outputterminal of the frequency divider 12. The movable contact of the firstswtich 40A is connected to one fixed contact of the second switch 40B,the other fixed contact of which is connected to the output terminal ofthe frequency divider 13, and the movable contact of which is connectedto the divider chain 20. Double throw switches associated with othertone generators representing the notes C to B are connected in the samemanner. The coils of the aforesaid ers 15, 16 and. 17 corresponds to thecase where the student stations each consist of a 49-key electronicmusical instrument.

Where the teacher operates the triple throw switch 14 to connect themovable contact to the fixed contact a, there are obtained four outputtone signals A,.B, C and D corresponding to the notes C C C and C,respectively. Namely, the student stations are set to have a relativelyhigh compass as C, to C Where the teacher operates the triple throwswitch 14 to connect the movable contact to the fixed contact b, thenthe student stations make a performance with a relatively medium compassasC to C And where the movable contact is connected to the fixed contactc, then the student stations make a performance with a relatively lowcompass as C to C The teacher station has 12 triple throw switches 14 tomatch all the notesC, through 8,. It is preferred for simplification ofthe teachers operation that the 12 triple throw switches 14 be designedto interlock each other as shown in FIG. 1.

Twelve interlocking triple throw switches, however, will have anextremely complicated construction. Therefore, it is desired that theinterlocking switches be relays 41A and 41B are connected at one end tothe movable contact of the triple throw switch 14 through a power source42, and at the other end to the fixed contacts b and c, respectively, ofthe triple throw switch 14. Another fixed contact switch a of the triplethrow switch 14 remains empty. The condition where the double throwswitches 40A and 40B are in the indicated position denotes that wherethe relays 41A and 41B are not energized, namely, where the movablecontact of the triple throw switch 14 contacts its empty fixed contacta.- Since, at this time, an output from each tone generator is directlysupplied to the corresponding divider chain, the student stations areset to make a high compass performance. Where the movable contact of thetriple throw switch 14 is made by the teachers operation to contact thefixed contact b connected to the relay 41A for its energization, thenthe movable contact of the firstdo'uble' throw switch 40A changes itsengagement from one fixed contact to the other. Under this condition,the student stations make a medium compass performance. Where themovable contact of the triple throw switch 14 contacts still anotherfixed contact c to energize the relay 413, then the movable contact ofthe second double throw switch 40B changes its engagement from one fixedcontact to the other, causing the student stations to play a lowcompass'performance.

' According to the tone generator arrangement shown in FIGS. 1 and 4,operation of thetriple throw switch 14 provided in the teacher stationcauses all the student stations to make a performance with the samecompass, thus presenting difficulties 'in effecting an ensembleperformance on the student stations. FIG. 2 indicates the arrangementwhereby the student stations can attain an ensemble performance evenwhen the students operate the same part of the keyboard. In a grouptraining system according to the embodiment of FIG. 2, student stationsare divided into' a plurality of groups. There are provided dividerchains 20-1 to 20-n each arranged like that of FIG. 1 in the same numberas the groups of student stations. As in the embodiment of 4 Where thetriple throw switches 14-1 to l4-n are in the indicated state, thestudent stations of the first and second groups are set to makea highcompass performance, the third group to play a medium compassperformance and the group of the n-th order to produce a low compassperformance. Accordingly, the arrangement of FIG. 2 enables the variousgroups of student stations to play performances with differentcompasses, that is, an ensemble performance collectively while all thestudents operate the identical part of the keyboards.

The embodiment of FIG. 3 has an arrangement capable of displaying abetter ensemble performance. According to this embodiment, the dividerchains -1 to 20-n for the tone generator corresponding to the note C areselectively supplied with tone signals corresponding to the G notes asshown or alternatively E notes displaced or transposed five or threedegrees from the C notes so as to have good musical agreements with theC notes. Thus the divider chains 20-1 to 20'-n are selectively suppliedwith outputs from the frequency dividers 24 and 25 associated with thetone generator 23 of the note G (or E included in the teacher stationand outputs from the frequency dividers l2 and 13 associated with thetone generator 11 of the tone C The other tone generators 11 arelikewise as sociated with the tone generators 23 whose pitches are fiveor three degrees displaced from those of the for met. The embodiment ofFIG. 3 also includes series connected double throw switches 26 and 27.The first double throw switch 26 is used to choose the pitch of tonesignals from the tone generator 11 and the second swtich 27 to choosethe note of tone signals from either of the tone generators 11 and 23,that is, tone signals representing either the C or G notes. Where thedouble throw switches 26 and 27 are in the indicated state, the dividerchain 20-1 is supplied with a note C tone signal from the frequencydivider 12, the divider chain 20-2 with a note C tone signal from thefrequency divider 13, the divider chain 20-3 with a note G tone signalfrom the frequency divider 25 and thedivider chain 20-n with the sametone signal as that supplied to the divider chain 20-1. In this case,therefore, the third group of student stations can make a performancewhose pitch is displaced or disposed five'degrees from that played bythe other groups, through the students of the third group depress thesame part of the keyboard as that operated by the students of the othergroups. 1

In the case of the aforesaid embodiments, the students have to recognizeby their auditory sense the compasses played by themselves, when theteacher varies the compasses played by the students. However, it isdifficult for'the students to discriminate thecompasses with which theyare making a performance. Accordingly, it will be more desirable if thestudents can visually judge which of the high, medium and low compassesis adopted for the performance played by. themselves.

To this end, the group training system of this invention includes aplurality of indicators or lamps disposed adjacent to the keyboard ofeach student station. One of the lamps is turned on in accordance withteachers operation to change the compass of the student stations,thereby assisting the students in distinguishing the compass with whichthey are making a performance.

6 FIG. 5 is a plan view of an electronic musical instrumentconstitutinga student station. Where the student station consists of afour-octave or 49-key electronic musical instrument, there are fittedthree lamps 52, 53 and 54 to a bar 51' disposed adjacently to thekeyboard 50. These lamps are spaced at an interval correspond ing to oneoctave. The keys 55, 56 and 57 facing the lamps denote particular notes,in this case, C notes. The key facing a lighted lamp further representsa reference note C Where the teacher operates to change the compass ofthe performance on the student stations to a high level, the lamp 52 onthe extreme left alone is turned on. Since the key 55 facing the lamp 52denotes the note C the students can recognize that they are playing aperformance with a high compass. In the case of this high compassperformance the keys 56 and 57 correspond to the notes C and C,respectively. Where there is played a performance with a medium compass,the lamp 53 alone is operated. From the fact that the key 56 facing thelamp 53 corresponds to the note C the students are informed that theyare playing a performance with a medium compass. In the case of a lowcompass performance, the lamp 54 on the extreme right alone is lighted,indicating that the student stationsare making a low compassperformance. The foregoing description is based on the fact that anoutput A from the triple throw switch 14 of FIG 1, outputs B and C fromthe frequency dividers 15 and 16 respectively are supplied to keyswitches actuated by the keys 57, 56 and 55 facing the aforesaid lamps54, 53 and 52.

FIG. 6 illustrates a circuit for selectively turning on any oneof thethree lamps 52, 53 and 54. The teacher station 1 further includesanother triple throw switch 60 for lamp indication interlocking theaforesaid triple throw switch 14 anda power source 61. The three fixedcontacts of the lamp indication triple throw switch 60 are connected bycable to one end of the lamps 52, 53

1 and 54 and the movable contact of the swtich 60 is connected similarlyby cable to the other ends of the lamps through the power source-61 Thelamp indication circuit of FIG. 6 requires the same number of cables asthe lamps for each student station 2. Where, therefore, there areprovided many student stations, the work of connecting the cables willbe accompanied with great difficulties.

FIG. 7 shows a lamp indication circuit free from the drawbacks of thecircuit of FIG. 6. According to the embodiment of FIG. 7, there isconnected in parallel with a power source 62 of the teacher station 1 atriple throw switch 60 for lamp indication interlocking the aforesaidtriple throw switch 14. The fixed contact a of the lamp indicationswitch 60 is connected to the positive terminal of the power source 62and the fixed terminal c is connected to the negative terminal thereof,

namely, to the ground, whereas the fixed contact b of the switch 60remains idle. The positive terminal of the power source 62 and themovable contact of the'lamp indication switch 60 are connected. by cableto the student stations 2. t

In the student stations, there are connected in series between the powersource positive terminal line 63 and ground the collector-emittercircuit of an NPN transistor Tr, and that of a PNP transistor Tr withthe emitters connected with each other, the bases of which are connectedto the movable contact line 64 of the lamp indication switch 60.

To the emitters of the transistors Trl and'Tr2 is connected a firstcontrol means 65 including PNP transistors Tr and Tr,,. The base of thetransistor Tr is connected to the emitter of the transistor Tr and thebase of the transistor Tr., to the collector of the transistor Tr Thecollector-emitter circuits of the transistors Tr' and Tr, are connectedbetween the positive terminal line 63 and ground. To the collectorcircuit of the transistor Tr is connected a first indicator or lamp 52.

The collector-emitter circuits of a PNP transistor Tr and an NPNtransistor Tr constituting a second control means 66 are connectedinseries between the positive terminal line 63 and ground. A secondindicator or lamp 53 is connected between the collectors of thetransistors Tr, and Tr,,. The bases of both transistors Tr and Tn, areconnected to the emitter of the transistor Tr The collector-emittercircuits of NPN transistors Tr, and Tr constituting a third controlmeans 67 are connected between the positive terminal line 63 and ground.The base of the transistor Tr, is connected to the emitter of thetransistor Tr and the base of the transistor Tr to the collector of thetransistor Tr,. A third indicator or lamp 54 is connected to thecollector of the transistor Tr Where, in the circuit of FIG. 7, themovable contact of the lamp indication switch 60 is connected, as shown,to the fixed contact a, the transistor Tr, is turned on and thetransistor Tr, is turned off. Under this condition, the transistor Tr,included inthe first control means 65 is rendered nonconductive and thetransistor Tr, included therein is rendered conductive. The'transistorsTr, and Tr of the second control means 66 are turned off andonrespectively. The transistors Tr, and Tr, of the third control means 67are turned on and off respectively. in this case, therefore, the firstlamp 52 alone is obviously lighted.

Where the movable contact of the lamp indication switch 60 is connectedto an idle fixed contact b, then the transistors T r,, Tr Tr and Tr, arerendered nonconductive and the transistors Tr Tr Tr and Tr, are renderedconductive. In this case, the second lamp 53 alone is lighted.

Where the movable contact of the lamp indication switch 60 contacts thefixed contact c, then the transistors Tr Tr Tr and Tr, are turned offand the transistors Tr Tr Tr, and Tr are turned on, thus operating thethird lamp 54 alone. As apparent from the foregoing description,combinations of the different conductivity type transistors constitutingthe first to third control means enable any one of the three lamps to beselectively lighted. v

What is claimed is:

1. In a group training system for musical instruments including a singleteacher station and a plurality of student stations formed of keyboardmusical instruments comprising:

each of said student stations having a multi-octave keyboard with a keyswtich for each key of said keyboard, and said teacher stationcomprising: a plurality of tone generators providing the tones of oneoctave of the chromatic scale; each of said tone generators having anoutput terminal connected to a first chain of cascaded frequencydividers, each of said frequency dividers having an output terminal;

8 swtiching means having a plurality of inputs connected, respectively,to each of said output terminals and having an output connected to asecond chain of frequency dividers, said switching means operative toselectively connect one of said inputs to said output; 1 said secondchain of frequency dividers comprising a plurality of cascaded frequencydividers whose outputs are connected to said key switches on saidstudent keyboard corresponding to respective octaves of the tone of saideach tone generator.

2. The group training system according to claim 1 wherein said frequencydividers constituting the first and second divider chains divide thefrequency of input signals by two.

3. The group training system according to claim 1 wherein each of saidstudent stations includes a plurality of indicators positioned adjacentto the. keyboard and a plurality of control means each provided with acontrol terminal and connected in series to said indicators across apower source; and said teacher station includes a second switching meansinterlocking said switching means between said first and second dividerchains and having a movable contact and the same number of fixedcontacts as said plural control means, said fixed contacts being soconnected as to have different potentials and said movable contact beingconnected to the control terminal of each of said plural control means,thereby impressing a control potential on the control terminals of allsaid plural control means according to the condition of said switchingmeans so as to give'and indication to-theindicators.

4. The group training system according to claim 1 wherein said teacherstation further includes a plurality of second tone generators bearing aparticular musical relationship with said first tone generators; and athird divider chain corresponding to one of said second tone generatorsand including a plurality of cascade connected frequency dividers andconnected to said one of said second tone generators, the output"terminal of at least one frequency divider included in said thirddivider chain being connected to at least one of the inputs of theswitching means.

5. The group training system according to claim 1 wherein each of saidstudent stations includes a pluralityof indicators disposed adjacent tothe keyboard; and

said teacher station includes a second switching means interlocking theswitching means between said first-and second divider chains andselectively giving an indication to said indicators.

6. The group training system according to claim 5 wherein said secondswitching means is provided with a plurality of fixed contacts eachconnected to each of the indicators, and with a movable contactconnected to the indicators through a power source.

7. The group training system according to claim 5 wherein saidindicators are so disposed as to facethe keys on the keyboardcorresponding to predetermined notes.

8. The group training system according to claim 5 wherein said studentstations each include first, second and third indicators and first,second and third control means; and wherein said first control meansincludes first and second transistors of a first conductivity type whichare so connected that while said first transistor is renderedconductive, said second transistor is rendered nonconductive by basebias voltages, the base of said first transistor being connected to saidmovable contact of said second switching means and the collector-emittercircuit of said second transistor being connected to said firstindicator, said second control means includes third and fourthtransistors of a second conductivity type different from said firstconductivity type, said third and fourth transistors being so connectedthat while said third transistor is rendered conductive, said fourthtransistor is rendered nonconductive by base bias voltages, the base ofsaid third transistor being connected to said movable contact of saidsecond switching means and the collector-emitter circuit of said fourthtransistor being connected to said second indicator, and said thirdcontrol means includes a fifth transistor of said first conductivitytype and a sixth transistor of said second conductivity type, said fifthand sixth transistors having their collector-emitter circuits connectedin series in the forward direction, the bases of fifth and sixthtransistors being connected to said movable contact of said secondswitching'means and said third indicator being connected between thecollector-emitter circuits of said fifth and sixth transistors.

9. The group training system according to claim 8 wherein said firstconductivity type is an NPN type and said second conductivity type is aPNP type.

10. The group training system according to claim 8 which furthercomprises a seventh transistor of said first conductivity type and aneighth transistor of said second conductivity type, said seventh andeighth transistors having their collector-emitter circuits connected inseries in the forward direction, said movable contact of said secondswitching means being connected to the bases of said seventh and eighthtransistors, and electrodes of said seventh and eighth transistorsconnected to each other being connected to the bases of said first,third, fourth and fifth transistors included in said first, second andthird control means.

11. In a group training system for musical instruments including asingle teacher station and a plurality of groups of student stationsformed of keyboard musical instruments comprising:

each of said student stations having a multi-octave keyboard with a keyswitch for each key of said keyboard, and

said teacher station comprising:

a plurality of tone generators providing the tones of one octave of thechromatic scale;

each of said tone generators having an output terminal connected to afirst chain of cascaded frequency dividers, each of said frequencydividers having an output terminal;

a plurality of swtiching means, each of said switching means having aplurality of inputs connected, respectively, to each of said outputterminals and having an-output connected to a second chain of frequencydividers, said switching means operative to selectively connect one ofsaid inputs to said out P said second chain of frequency dividerscomprising a plurality of cascaded frequency dividers whose outputs areconnected to each respective group of said student stations to said keyswitches on said keyboard corresponding to respective octaves of thetone of said each tone generator.

1. In a group training system for musical instruments including a singleteacher station and a plurality of student stations formed of keyboardmusical instruments comprising: each of said student stations having amulti-octave keyboard with a key swtich for each key of said keyboard,and said teacher station comprising: a plurality of tone generatorsproviding the tones of one octave of the chromatic scale; each of saidtone generators having an output terminal connected to a first chain ofcascaded frequency dividers, each of said frequency dividers having anoutput terminal; swtiching means having a plurality of inputs connected,respectively, to each of said output terminals and having an outputconnected to a second chain of frequency dividers, said switching meansoperative to selectively connect one of said inputs to said output; saidsecond chain of frequency dividers comprising a plurality of cascadedfrequency dividers whose outputs are connected to said key switches onsaid student keyboard corresponding to respective octaves of the tone ofsaid each tone generator.
 2. The group training system according toclaim 1 wherein said frequency dividers constituting the first andsecond divider chains divide the frequency of input signals by two. 3.The group training system according to claim 1 wherein each of saidstudent stations includes a plurality of indicators positioned adjacentto the keyboard and a plurality of control means each provided with acontrol terminal and connected in series to said indicators across apower source; and said teacher station includes a second switching meansinterlocking said switching means between said first and second dividerchains and having a movable contact and the same number of fixedcontacts as said plural control means, said fixed contacts being soconnected as to have different potentials and said movable contact beingconnected to the control terminal of each of said plural control means,thereby impressing a controL potential on the control terminals of allsaid plural control means according to the condition of said switchingmeans so as to give and indication to the indicators.
 4. The grouptraining system according to claim 1 wherein said teacher stationfurther includes a plurality of second tone generators bearing aparticular musical relationship with said first tone generators; and athird divider chain corresponding to one of said second tone generatorsand including a plurality of cascade connected frequency dividers andconnected to said one of said second tone generators, the outputterminal of at least one frequency divider included in said thirddivider chain being connected to at least one of the inputs of theswitching means.
 5. The group training system according to claim 1wherein each of said student stations includes a plurality of indicatorsdisposed adjacent to the keyboard; and said teacher station includes asecond switching means interlocking the switching means between saidfirst and second divider chains and selectively giving an indication tosaid indicators.
 6. The group training system according to claim 5wherein said second switching means is provided with a plurality offixed contacts each connected to each of the indicators, and with amovable contact connected to the indicators through a power source. 7.The group training system according to claim 5 wherein said indicatorsare so disposed as to face the keys on the keyboard corresponding topredetermined notes.
 8. The group training system according to claim 5wherein said student stations each include first, second and thirdindicators and first, second and third control means; and wherein saidfirst control means includes first and second transistors of a firstconductivity type which are so connected that while said firsttransistor is rendered conductive, said second transistor is renderednonconductive by base bias voltages, the base of said first transistorbeing connected to said movable contact of said second switching meansand the collector-emitter circuit of said second transistor beingconnected to said first indicator, said second control means includesthird and fourth transistors of a second conductivity type differentfrom said first conductivity type, said third and fourth transistorsbeing so connected that while said third transistor is renderedconductive, said fourth transistor is rendered nonconductive by basebias voltages, the base of said third transistor being connected to saidmovable contact of said second switching means and the collector-emittercircuit of said fourth transistor being connected to said secondindicator, and said third control means includes a fifth transistor ofsaid first conductivity type and a sixth transistor of said secondconductivity type, said fifth and sixth transistors having theircollector-emitter circuits connected in series in the forward direction,the bases of fifth and sixth transistors being connected to said movablecontact of said second switching means and said third indicator beingconnected between the collector-emitter circuits of said fifth and sixthtransistors.
 9. The group training system according to claim 8 whereinsaid first conductivity type is an NPN type and said second conductivitytype is a PNP type.
 10. The group training system according to claim 8which further comprises a seventh transistor of said first conductivitytype and an eighth transistor of said second conductivity type, saidseventh and eighth transistors having their collector-emitter circuitsconnected in series in the forward direction, said movable contact ofsaid second switching means being connected to the bases of said seventhand eighth transistors, and electrodes of said seventh and eighthtransistors connected to each other being connected to the bases of saidfirst, third, fourth and fifth transistors included in said first,second and third control means.
 11. In a group training system formusical insTruments including a single teacher station and a pluralityof groups of student stations formed of keyboard musical instrumentscomprising: each of said student stations having a multi-octave keyboardwith a key switch for each key of said keyboard, and said teacherstation comprising: a plurality of tone generators providing the tonesof one octave of the chromatic scale; each of said tone generatorshaving an output terminal connected to a first chain of cascadedfrequency dividers, each of said frequency dividers having an outputterminal; a plurality of swtiching means, each of said switching meanshaving a plurality of inputs connected, respectively, to each of saidoutput terminals and having an output connected to a second chain offrequency dividers, said switching means operative to selectivelyconnect one of said inputs to said output; said second chain offrequency dividers comprising a plurality of cascaded frequency dividerswhose outputs are connected to each respective group of said studentstations to said key switches on said keyboard corresponding torespective octaves of the tone of said each tone generator.